1. Field of the Invention
The present invention relates to a speed reducer that reduces the speed of input rotation and outputs the reduced rotation.
2. Description of the Related Art
Conventionally, a geared motor GM1 illustrated in FIG. 3 is known (see Japanese Patent Laid-Open Publication No. 2001-323972). The geared motor GM1 is composed of a motor M1 and a speed reducer G1 connected together.
The motor M1 is secured on a motor fixture 2, which is secured on a first carrier 11 by a bolt 21. A connection shaft 3, on which a pinion 4 is formed, is connected by a key to a motor axis 1 of the motor M1. This pinion 4 is in mesh with a gear 5. The gear 5 is integrally connected to a rotating axis 6 so as to rotate together. An eccentric body 7 is integrally formed on the rotating axis 6. The eccentric body 7 can oscillatingly rotate an external gear (a planetary gear) 9 with an eccentric body bearing 8 interposed therebetween. The external gear 9 is also in mesh with an internal gear 10. The number of teeth of the external gear 9 and that of the internal gear 10 are chosen such that the difference between the two is very small. The internal gear 10 also serves as a casing of the speed reducer G1 and is disposed and secured on a base 16 by bolts 19. The first carrier 11 is supported by a bearing 13 to rotate with respect to the internal gear 10. The first carrier 11 has an integrally formed carrier pin 11A. The carrier pin 11A is inserted with some play in a carrier pin hole 9A of the external gear 9. A second carrier 12 is connected to the carrier pin 11A by a bolt 15. This second carrier 12 is supported by a bearing 14 to rotate with respect to the internal gear 10. In other words, the first and second carriers 11 and 12 can rotate together as a whole with respect to the internal gear 10.
The base 16 has a flange 16A formed so as to extend inward, and a hollow pipe 17 is secured to the flange 16A by bolts 18. The hollow pipe 17 penetrates the center of the speed reducer G1 so that wires or the like 20 can be laid through.
In the speed reducer G1 provided to the geared motor GM1, a part at the highest level that requires lubrication is a part where the pinion 4 and the gear 5 are in mesh. Then, if the speed reducer G1 is to be lubricated with a liquid lubricant, the lubricant needs to fill at least to this meshed part of the pinion 4 and the gear 5 (level indicated by the A-A line, for example).
The speed reducer G1 has a space within itself that is formed by the base 16, the flange 16A, the hollow pipe 17, the first carrier 11, an oil seal 22, and the internal gear 10, and a lubricant can be accommodated in this space.
However, if, as mentioned above, the lubricant is poured up to the part that requires lubrication and is at the highest elevation (the A-A level), the possibility that the lubricant leaks from the oil seal 22 will increase. In other words, since the lubricant level (the A-A level) is higher than a level of the oil seal 22, the oil seal 22 is constantly subjected to a pressure (a pressure from the interior to the exterior of the speed reducer) corresponding to the “difference” in level.